Ships, fishnets and other underwater structures or equipment tend to attract aquatic organisms such as barnacles, mussels, and algae which interfere with an efficient operation of ships and cause a waste of fuels in ships or cause clogging and shorten the service life of fishnets. To prevent such attachment of life to underwater structures, it is common practice to coat the surfaces of the structures with an antifouling coating. As a representative antifouling coating heretofore in use, there is a matrix type antifouling coating comprising a formulation of a rosin and a vinyl or alkyd resin which is insoluble in seawater. However, since a coating of this type releases an antifoulant ingredient together with the rosin into the seawater, a long-term stable antifouling effect cannot be expected and, moreover, since the insoluble resin remaining in the coating film forms a skeletal structure, the coating has the disadvantage that particularly when it is applied to ships, the resistance between the seawater and the coated surface is increased to slow down the speed of ships.
In recent years, in view of the long-term antifouling effect and other advantages, hydrolyzable antifouling coatings have been utilized widely and, as one variation, a coating comprising a metal-containing resin composition has been developed. Metal-containing resins in which a pendant acidic group and a monobasic organic acid form a salt with a metal atom and methods for producing the resins have been described in the patent applications filed by the present applicant, inter alia, Japanese Kokai Publication Sho-62-101653, Japanese Kokai Publication Sho-63-128008, Japanese Kokai Publication Sho-63-128084 and Japanese Kokai Publication Hei-08-73536. When a resin of this kind is used in an antifouling coating, the resin is gradually hydrolyzed in seawater to release the antifoulant metal ion and, at the same time, the resin itself is solubilized and eluted out to exhibit a self-polishing effect.